The LCD (Liquid Crystal Display) possesses advantages of thin body, power saving and no radiation to be widely used in many application scope. Most of the liquid crystal displays on the present market are back light type liquid crystal display devices, which comprise a liquid crystal display panel and a back light module. Generally, the liquid crystal display panel comprises a CF (Color Filter) substrate, a TFT (Thin Film Transistor) substrate, LC (Liquid Crystal) sandwiched between the CF substrate and TFT substrate and sealant. The working principle of the liquid crystal display panel is to locate liquid crystal molecules between two parallel glass substrates. By applying driving voltages to control whether the liquid crystal molecules to be changed directions, and changing the polarization of the light of the backlight module, and achieving the penetration or stop of the light path with polarizer, the objective of display can be realized.
The polymer dispersed liquid crystal (PDLC) as being liquid crystal light valve, has been widely concerned and used in the recent years. It is to mix the low-molecular liquid crystal and the prepolymer, in certain condition with polymerization, to form micron liquid micro drops to be evenly distributed in the high polymer network. Then, the dielectric anisotropy of the liquid crystal molecules are utilized to obtain the material with electro-optical property, which mainly works between the scatter state and the vitreous state and possesses a certain gray scale. The working principle is: in condition without applied voltage, a regular electrical field cannot formed between the PDLC thin films, and the light axis of the liquid crystal micro particle is orientated randomly and shows the disordered state. The refractivity and the refractivity of the polymer do not match, and the incident light is intensely scattered, and the PDLC thin film appears to be opaque or semitransparent; after the external voltage is applied, the light axis of liquid crystal micro particle is aligned to be perpendicular with the thin film surface, i.e. consistent with the electrical field direction. The refractivity of the liquid crystal micro particle and the refractivity of the polymer basically match. No obvious interfaces exist in the film to construct a substance which basically is uniform. Therefore, the incident light will not be scattered, and the PDLC thin film appears to be transparent. Besides, under the driving of the applied electrical field, the PDLC film possesses light switch property, and the transparency is raised along a certain curve with the increase of the applied voltage.
Besides, quantum dot (QD) as being a new raising display material has already been widely approved and concerned. The quantum dot is quasi-zero-dimensional nano material, which is constructed with a small amount of atoms. Roughly speaking, the sizes of the three dimensions of the quantum dot are all below 100 nanometer (nm), and the appearance is like an extremely tiny spot substance. The movements of the inner electron in respective directions are all restricted. The quantum confinement effect is particularly obvious. It possesses excellent properties that the excitation spectrum is wide and the distribution is continuous but the emission spectrum is narrow and symmetrical, and the color is adjustable, and the color chemical stability is high, and the fluorescence lifetime is long, and it is an ideal light emitting material. There are two different major types in the present quantum dots according to the acquirement of the energy. One is photoluminescence, and the other is electroluminescence. The light color of the quantum dot meets the size effect of the quantum dot, i.e. by controlling the shape, structure and size of the quantum dot, the electron statuses, such as the energy gap, exciton binding energy, exciton energy blue shift can be adjusted. With the gradual size decrease of the quantum dot, the light of the quantum dot is absorbed, and the spectrum blue shift phenomenon appears. As the size gets smaller, the spectrum blue shift phenomenon becomes more obvious.